Magnesium aluminate gallate phosphor

ABSTRACT

MAGNESIUM ALUMINATE GALLATE PHOSPHORS ACTIVATED BY MANGANESE ARE PREPARED CONTAINING A MINOR ADDITION OF STABILIZER ION TO AVOID BRIGHTNESS LOSS WHEN THE PHOSPHOR IS HEATED IN THE AIR. THE STABILIZER ADDITION ALSO PERMITS MAJOR SUBSTITUTION OF AL FOR GA ALONG WITH INCREASED MANGANESE ACTIVATOR CONTENT RESULTING IN HIGHER POWDER BRIGHTNESS AT ROOM TEMPERATURE, GREATER ULTRAVIOLET ABSORPTION, AND A DESIRABLE SHIFT IN SPECTRAL PEAK OF EMISSION RESPONSE ALONG WITH THE BETTER RESISTANCE TO OXIDATION WHEN HEATED IN AIR. THE PHOSPHOR IS PARTICULARYL USEFUL IN LOW PRESSURE MERCURY LAMPS FOR REPROGRAPHIC APPLICATIONS.

.30 Pf@ MOLE MUM//VTE GLLHTE E2 5 uw L 2 Kul KAt m` EMS Enum .w U. Mwr a m m, E 0. w Ju A M0 www nl 1 0 0 nu 0 0 0 H m 9 8 7 l l l l C W HALO -PHOSPHOE /.0 /.Z TE GFLLHTE MOLE My PEE MOLE HLLUM//V/Q United States Patent O 3,838,060 MAGNESIUM ALUMINTE GALLATE PHOSPHOR Edward E. Kaduk, Lyndhurst, Ohio, assignor to General Electric Company Continuation-impart of abandoned application Ser. No.

194,449, Nov. 1, 1971. This application Sept. 18, 1972,

Ser. No. 290,166

Int. Cl. C09k 1/36, 1/68 U.S. Cl. 252-301.4 P 4 Claims ABSTRACT F THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to luminescent materials and more particularly green-emitting magnesium aluminate gallate phosphors activated by manganese. This application is a continuation-in-part of my copending application entitled, Magnesium Aluminate Gallate Phosphor, Ser. No. 194,449, and tiled Nov. 1, 1971, now abandoned.

l Magnesium gallate activated by manganese emits in the green is described in U.S. Pat. 3,407,325 to J. l. Brown, J r., as particularly suitable for fluorescent lamps intended for reprographie applications such as Xerographic copying machines. W. L. Wanmaker et al., in an article appearing in Philips Research Reports, 22, 304-308, lune 1967, modified the formulation suggested by Brown in substituting a small amount of aluminum for gallium and observed a shift in the excitation band to shorter wave lengths and a rise in the quenching temperature.

In U.S. Pat. 3,499,843 to J. J. Brown, lr. et al., cathodoluminescent magnesium aluminate gallate phosphors are proposed having the spinel crystal structure and coming under the general formula MgXAl2yGa2(1 y)O3+X+zzMnz, wherein x `is between 0.25 and 1.10, y is between 0.0005 and 0.79, and z is between 0.0001 and 0.1. In the foregoing, y is the atom fraction of Al substituted for Ga, andV ice Aluminum being much cheaper than gallium, it is economically advantageous to substitute the former for the latter. According to the prior art, when small amounts of aluminum are substituted for gallium, the phosphor has p greater chemical stability and resistance to oxidation at high temperatures. However, when y is increased above 0.2 in compositions activated with 0.01 Mn+2 ion, brightness of the phosphor decreases rapidly. Thus, the advantages from substitution of aluminum for gallium in magnesium aluminate gallate phosphors up to now have been minimal and limited to a low proportion of A1 substitution.

Finally, it has been customary in the preparation of thse phosphors to employ ring temperatures as high as 1400 C. in order to derive an acceptable brightness level for the emission response. Such elevated firing temperatures necessitate the use of costly preparation containers such as platinum and often result in a phosphor material so hard and coarse that specialized additional treatment becomes necessary to prepare the final product.

Phosphors prepared as described in the prior art have given an acceptable performance when incorporated in the lamps intended for reprographie use. However, the requirements for this application have become even more stringent and thus further improvements are both necessary and desirable. The modifications which are described below permit attainment of these aims.

SUMMARY OF THE INVENTION Characteristics desirable in a phosphor intended for electrical lamps are high brightness and resistance to oxidation at the high temperatures that are encountered in lamp manufacture. High temperatures are encountered at lehring when the lamp envelope is heated to about 550 C. in air in order to decompose and drive out the binder usedto apply the phosphor, and also its sealing in exhaust of the lamp envelope. The phosphor should be able to withstand such heating without loss of brightness or other desirable characteristics. I have discovered that a startling improvement in the desirable characteristics of magnesium aluminate gallate manganese-activated phosphors is achieved by adding a minor proportion of a stabilizer ion producing substance to the phosphor ingredients prior to ring with said stabilizer ion being selected from the group consisting of an alkaline earth metal ion, a phosphate ion, and combinations of an alkaline earth metal ion with a phosphate ion. One class of stabilizer ion which avoids brightness loss when the phosphor is heated in the air and permits lower firing temperatures in the phosphor preparation is the P043 ion which can be obtained from Various additives, such as (NH4) ZHPO., and MgNH4PO4. A second class of stabilizer ion is the alkaline earth metals, especially the Ca)r2 ion which also can be obtained from various additives such as CaSO4. An especially preferred third class of the stabilizer is the combination of an alkaline earth metal ion with phosphate ion which can be obtained with such additives as CaHPO4 a cool white halophosphor, SrHPO4, and Bal-1F04. When the P04r3 ion is the ion or is Iused in combination with calcium ion, especially at concentrations containing .05 mole calcium ion per mole of the magnesium aluminate-gallate then still other benefits are obtained which are summarized in the following paragraphs below:

(1) The 1400 C. two-step firing temperatures conventionally employed in the phosphor preparation can be reduced significantly to approximately 1250 C. without experiencing signiiicant reduction in the powder brightness. The lowering of the firing temperatures will prolong furnace and phosphor container life as well as permit the substitution of lower cost container materials such as quartz or Vycor trays in place of platinum vessels. Additionally, the air firing at these lower temperatures enables more effective control of the phosphor particle size which is desirable for use in reprographie lamps.

(2) The spectral peak `of emission response for the present phosphors can be shifted toward the blue end of the spectrum without experiencing brightness loss. This proves to be an advantage for high speed xerographic reproduction since the process is more sensitive in the blue region. The eiect is especially useful to offset a color shift from 505 nanometers to 512 nanometers in emission peak which otherwise occurs with increasing Al substitution in the phosphor. The brightness of emission response can also be improved by increasing the Mnt2 activator level when a CaHPO4 additive is employed in accordance with practice of the present invention.

(3) Particularly useful phosphor compositions of the present invention contain higher proportions of aluminum substitution for gallium wherein y=0.3 and higher (0.3 atom fraction A1 substituted for Ga) and further contain at least 0.03 mole Mn+2 per mole magnesium aluminategallate and greater. The higher Al substitution without accompanying brightness loss is advantageous from a cost standpoint, especially when considered in conjunction with lower tiring temperatures which are also thereby possible.

A still further advantage derived by practice of the present invention is greater permissible variation in the phosphor composition with respect to other consttuentsv in the composition such as the Mgt2 ion content for preparation of high brightness phosphors in a wider range of phosphor particle size than is otherwise obtainable. In this regard it has been found that whereas Ca doping of a phosphor composition containing a manganese concentration of 0.03 mole Mn+2 ion per mole magnesium aluminate-gallate with 0.3 atom fraction of Al being substiuted for Ga should be kept below .05 mole Cai*2 ion per mole magnesium aluminate-gallate to improve the phosphor powder brightness, it is now possible to extend the additive range without a significant decrease in brightness to a wider concentration limit between about 7.5X 10-2 and 2.1 10'-1 mole of phosphate ion per mole magnesium aluminate-gallate when the phosphate ion is used as the only stabilizer ion or is used in combination with an alkaline earth metal ion. It was also found that for the especially preferred additives which contain both phosphate ion and Ca+2 ion there can be a mole ratio of alkaline earth metal ion to phosphate ion between approximately 1-1.6.

DRAWINGS AND DETAILED DESCRIPTION FIG. 1 is a graph showing the variation in powder brightness with phosphate ion concentration in a phosphor according to the present invention.

FIG. 2 is a graph showing the variation in powder brightness with calcium ion concentration for the otherwise same phosphor composition reported in FIG. 1 and which further shows the degree of oxidation resistance provided by the Ca+2 ion additive.

FIG. 3 is a graph showing the variation in powder brightness with magnesium ion concentration in a phosphor of the present invention and which further depicts the variation obtained with the firing temperatures ernployed in phosphor preparation.

Tables 1-12 present the results of tests on magnesium aluminate gallate phosphors.

TABLE N O. 1

Powder Brightness ot Mg Alumnate-Gallate Oxidation resistance test Original phosphor (7.5 ruin. at 550 C.)

Percent Percent Percent Percent Percent Emission Test Y brightness U.V. abs. brightness U.V. abs. loss peak, nm.

.01 mole Mn/mg(Ga,A1)z04 15...-.. MgGaLlmOi 0. 1 100. 0 81.5 89.7 81. 9 10. 3 505 B Mg Gai .1Alo.s04 0. 15 102. 5 79. 8 93.8 79. 2 8. 7 505 0....- Mg Gai A101104 0. 3 94. 1 69. 5 90. 4 69. 5 3. 7 507 D...... MgGm.uA11.o0| 0. 5 62. 5 43. 5 61. 7 45. 0 0. 8 512 .03 mole Mn/mg(Ga,A1)zO4 15..... MgGai.4A1o.a04 0. 3 107.3 85. 5 98. 4 84. 3 8. 9 512 .08 mole Mn/mg(Ga,Al)zO4 F.... MgGaoeAlLiOi 0.7 38. 2 49. 0 33. 7 50.0 4. 5 522 TABLE N O. 2

Powder Brightness ot Mg Aluminate-Gallate with Calcium Halophosphate Addition (All air rings at 1,400 C.)

.03 mole Mn/MgGa1.4Aiu.O4 (y=0.3)

Oxidation resistance test Original phosphor (7.5 min. at 550 C.)

Mole CaO per mole alumlnate- Percent Percent Percent Percent Percent Emission galiate brightness U.V. abs. brightness U.V. a s. loss peak, nm.

None 107. 3 85. 5 98. 4 84. 3 8. 9 512 3X1O5- 107. 8 8G. 5 103. 0 86. 5 4. 8 510 1x10-3-.. 112.0 91. 5 108. 7 91. 5 3. 3 510 5X10`5 115.0 90.0 112. 5 90. 1 2. 5 511 2)(107 117.0 91. 7 114. 5 91. 5 2. 5 511 1.35)(10-1. 101. 0 93. 9 99. 7 94. 2 1. 3 513 TABLE N0. 3

Powder Brightness of Mg Aluminate-Gallate .03 mole Mn/MgGa1-4Alq.o04 (Y=0.3)

Oxidation resistance test Original phosphor (7.5 min. at 550 C.)

Mole MO per mole aluminate- Percent Percent Percent Percent Percent Emission galiate brightness U.V. abs. brightness U.V. abs. loss peak, nm.

With Calcium Carbonate Addition 4)(10-s 115. 5 93. 1 114. 5 93. 3 1. 0 511 8X10-f 112. 0 93. 1 109. 5 92. 3 2. 5 511 with calcium Acid Phosphate Addieren Lexia-1 117. o 92. o 115. 5 92. 4 1. 5 511 6.7 X102 118. 5 92. 4 116. 0 92. 4 2. 5 511 With Strontium Acid Phosphate Addition Mole SrO 1.9)(10-z 112.0 86. 7 103. 5 87.0 8. 5 511 With Barium Acid Phosphate Addition Mole BaO 1.9 10a 109. 5 83. 5 101. 0 83.5 8.5 511 *M stands for Ca, Sr, or Ba: l

TABLE NO. 4

Powder Brightness of Mg Aiuminate-Gallate with Calcium Addition .04 mole Mil/MgGar-zAlmOi (Y=0.4)

Oxidation resistance test Original phosphor (7 .5 min. at 550 C.) l

Mole CaO per mole alumnate- Percent Percent Percent Percent Percent Emission gailate brightness U.V. abs. brightness U.V. abs. loss peak, nm. 5x10x (CW Halo) 106. 0 85. 7 104. 5 85. 3 2. 0 511 6.7 X10-2 (CaHPO4) 114. 2 90.7 112.0 90. 8 2. 2 512 TABLE NO. 5

Z mole Mn/MgGa1.oAli.0.04 (y=0.5)

Oxidation resistance test Original phosphor (7.5 min. at 550 C.)

' Emission Mole CaO per mole Percent Percent Percent Percent Percent peak, aluminate-gallate Z brightness U.V. abs. brightness U.V. abs. loss nm. None 01 62. 5 43. 61. 7 45. 0 0. 8 512 9.5)(10-4 (CW Ha1o) 03 89. 2 Y 72. 7 86. 8 69. 2 2.4 517 1.6X10-3 (CW Halo) .03 91.3 71. 3 87. 2 70.2 4.1 515 5.0)(10-a (CW Haio). .03 95.5 70. 3 95.0 70.3 0. 5 513 6.7X102 (CaHPO4) 04 110. 5 81. 8 n 109.5 82.5 1. 0 513 With SrHPO Addition 6.7)(102 (SrHPO) .04 100. 2 75.4 97. 0 75.0 3. 2 514 TABLE NO. 6

Etect of Calcium Addition on Mg Aiuminate-Galiate Having Very High Manganese Content Oxidation resistance test Original phosphor (7.5 min. at 550 C.) Mole CaO per mole Percent Percent Percent Percent Percent Emission aiuminate-gallate Z brightness U.V. abs. brightness 'U.V. abs. loss peak, nm. None 08 38. 3 49. 0 33. 7 50. 0 4. 6 522 6.7)(10-2 (CaHPO4) 08 62. 5 59. 0 57. 8 61. 0 4. 7 522 6.7)(10-2 (CaHPO4) 12 32. 5 67. 2 29. 6 66. 7 2. 9 523 TABLE NO. 7 Eect of Variation of Magnesium in Mg Aluminate-Gailate with Calcium Addition MgxGai.4A1o.a0|+x:Mn.oa;Ca.oz (Y=03) Oxidation resistance test Original phosphor (7.5 min. at 550 C.) Percent Percent Percent Percent Percent Spectral :r brighthess U.V. abs. brightness U.V. abs. loss peak, nm. 22. 5 91. 1 22. 0 91.7 0. 5 515-516 117. 0 91.7 114. 5 91. 5 2. 5 511 115. 0 88. 5 107. '5 89. 6 7. 5 510 109. 0 90. 1 98. 5 89. 9 10. 5 510 Powder Brightness of Mg Aluminate-Geliate With Various Additives .03 mole Mn/MgGa14Aiu-O4 (y=0.3) :Mw=moie additive Oxidation resistance test Original phosphor (7.5 min. at 550 C.)

Percent Percent Percent Percent Percent Emission .Air firing temp., C. Mw brightness U.V. abs. 'brightness U.V. abs. loss peak, nm.

(A) 1,400 None 107. 5 85. 5 98. 5 84. 5 9. 0 512 (B) 1,250 None 86.5 72. 5 79. 5 72. 5 7. 0 511 Mw= CaHP O4 (C) 1,250 .18 112.0 87.0 108. 5 87. 5 3. 5 508 Mw= (Nimmo.

Mw=MgNH4PO4 Mw= CaCO;

Mw=CaSO4 TABLE NO. 9

Powder Brightness of Mg AluminateGa1iate With (N H4)2HPO4 Additive .O3 mole Mn/Mg,a5Ga1,4A1u,c0s.a5(y=0.3):Mw=mo1e PO4/(GaA1)2O;

(A11 air filings at 1,250 C.)

Oxidation resistance test Original phosphor (7.5 min. at 550 C.)

Percent Percent Percent Percent Percent Emission Mw brightness U.V. abs. brightness U.V. abs. loss peak, nm.

None 86. 5 72. 79. 5 72. 7. O 511 1. 8X10s 89. 5 76. 0 83. 5 75. 2 6. 0 511 1. 8X10'z 98.5 81. 4 97. 3 82. 5 1. 2 510 1. 0X10I 110. 5 85. 5 109. 5 86. 0 1.0 510 1 8X10'l 109. 0 85. 0 104. 2 85. 0 4. 8 509 3. GX10-1 78. 5 78.5 79. 7 78.4 509 l Gain +1.2.

TABLE NO; 10

Powder Brightness of Mg Aluminate-Gailate with MgNH4PO4 Additive .03 111016 MD/MgxG81.4A1o.e0a+x:Mw=None (y=0.3)

(All air rings at 1,250 C.)

Oxidation resistance test Original phosphor (7.5 min. at 550 C.)

Percent Percent Percent Percent Percent Emission X brightness U.V. Abs. brightness U.V. abs. Loss peak, n m.

.03 mole Mn/MgxGa1.4A.i0.:Mw=.18 Mole MgNH4PO4/(GaADzO:

.03 mole Mn/MgGa1.4A1o.s:O41Mw=.28 mole mgNH4PO4/(GaAD2O3 TABLE NO. 11

Powder Brightness 0I Mg A1uminate-Ga11ate With Cool White Halo Additive .03 mole Mn/MgxGei.4A1o.u0a+x:MW=-02 m01@ Ca/(GBA-zol (Y=03) (Ca/PO4=1.6 for CW Halo) [All air rings at 1,400 C.]

Oxidation resistance test Original phosphor (7.5 min. at 550 C.)

Emission Percent Percent Percent Percent Percent peak, X brightness U.V. abs. brightness U.V. ebs. loss nm.

.03 mole Mn/MgasGai.4A1u.uO;.a5:Mw=N one G) None 107. 5 85. 5 98.5 84. 5 9.0 512 According to the brightness curves shown in the .Wanmaker paper, a preferred formulation wherein y=0.1 `1s: 1

Mgcs'zGaLsAlazOassMfllioi- 1 have used thisformulation to produce a phosphor to which I have assigned a brightness value of 100%. The brightness values reported in Tables 1-12 were also obtained by using eye-sensitivity iltering means with the photocell detector.

According to Wanmaker, when y: 0.1, the phosphor is '6% less bright at room temperature than the unsubstituted magnesium gallate; the phosphor wherein y=0.2 is already less bright, and the phosphor wherein y=0.4 is 55% less bright and thus practically useless. By means of a minor addition of an alkaline earth compound, I have greatly improved the brightness, oxidation resistance and general utilityv of these aluminum substituted gallate phosphors, as appears in Tables 1-6.

In Table 1, the results of tests on magnesium aluminate gallate phosphor with substitution of Al for Ga ranging from y=0.1 to 0.7 are given. These phosphors have been prepared according to prior art teachings without addition of any stabilizer ion containing material. The compositions are listed on the basis of one (1) mole Mg; however, as is well known, there is a denite loss of elemental Ga during the firing in a reducing atmosphere. For this reason, the original compounding is carried out with a lesser proportion of Mg in order that the iired ,product will conform more closely to the formula indicated.

It is apparent that the brightness of the phosphor decreases as the aluminum substitution is increased to y=0.3, 0.5, 0.7. Whereas the original phosphor brightness is 100% for test A wherein the Al for Ga substitution is y=0.1, the brightness drops to 62.5% in test D wherein the Al substitution is 0.5, and to 38.2% in test F wherein the Al substitution is 0.7. The ultraviolet absorption of the phosphor drops from 81.5% in test A to 43.5 %in test'D.

Considering now the brightness after the standard oxidation resistance test which consists in holding the phosphor at 550 C. for 7.5 minutes in air, test A shows a drop in brightness from 100.0% to 89.7% for an oxidation loss of 10.3%, whereas test D shows a drop in brightness from 62.5% to 61.7 for a loss of 0.8%. Tests C and E show that increasing the manganese concentration increases brightness but at the same time reduce oxidation resistance. Also part of the increase in brightness is due to the shift in the emission peak Wavelength, the light belower in fact that the phosphor is no longer useful. Higher manganese content improves brightness but reduces oxida- TABLE NO. 12

Powder Brightness of Mg Aluminate-Gallate With CaHPOi Additive 03 Mn/MgxGanAAlu,0Oa+x(y=0.3) Mw=mole Ca+2PO43/(GaAl)zO3 C Oxidation resistance test Onginal phosphor (7.5 niin. at 550 C.) Air Emission nn Percent Percent Percent Percent Percent peak, Mw X T., C brightness U.V. abs brightness U.V. abs ss nm.

(A.) None 1, 400 1U?. 5 85. 5 98. 5 84. 5 9. 0 512 (B) 02 85 1, 400 117. 0 92. 0 115. 0 92. 5 2. 0 511-512 (0)---" 07 85 1, 400 119. 0 92. 5 116.0 92. 5 3.0 510-511 (D) .18 75 1, 350 114.0 88. 0 110.0 90.0 4.0 506 4 (E) 28 65 1, 300 106. 0 85. 0 99. 5 85. 5 6. 5 508 .03 Mn/MgxGao.s4Aln.eOs+x .03 Mn/Mgx Gan.a4A1o.60a+x (G) 75 18 Practically dead-Faint red fluorescence tion resistance and shifts the emission peak towards the green.

In Table 2, the results of tests on magnesium aluminate-gallate having 0.3 substitution of Al for Ga, 0.03 mole Mn activation, and addition of a stabilizer material in the for-m of calcium halophosphate in the stated proportions starting at 0 and going up to l.35 10*1 mole of CaO per mole of magnesium aluminate-gallate are given. The additive consists of the well-known phosphor comymonly used in cool white uorescent lamps. The remarkable improvements produced by adding both calcium ion and phosphate ion to the phosphor according to my invention are apparent. In summary they are:

(l) Higher powder brightness at room temperatures, 117% compared with a phosphor having Al substitution of y=0.1 and 0.01 moles Mn per mole magnesium aluminate-gallate such as sample A in Table 1.

(2) Greater ultraviolet absorption, up to 94% compared with 78.82% for the phosphor having Al substitution of y=0.1.

(3) Better oxidation resistance upon heating in air. The standard test of 7.5 minutes at 550 C. shows a loss in brightness of 1% to 3% for the better samples, compared with a loss ranging from 10% to 15% typical of magnesium aluminate-gallate phosphors with Al substitution of y=0.1 prior to the invention.

These desirable improvements in brightness and resistance to oxidation achieved by adding both calcium ion and phosphate ion to the magnesium aluminate-gallate phosphor having Al substitution of y=0.3 and 0.03 mole manganese activation have been obtained without significantly altering the spectral distribution or the position of the emission peak.

In Table 3, the results of using other stabilizer additives according to the present invention are given. At the same vapproximate additive level the improvements in brightness and resistance to oxidation were best for CaHPO4 and the calcium halophosphate compared with a stabilizer additive containing Cai'2 ion as the only stabilizer additive or phosphate ion with a different alkaline earth metal.

Table 4 shows that the especially preferred additives are still eitective at a substitution of Al for Ga of y=0.4 and at a manganese content of 0.04 mole Mn+2 per mole magnesium aluminate-gallate. The brightness after the oxidation test is 106% to 114% and the oxidation loss in brightness is less than 3%.

Table 5 illustrates the relative eiiectiveness of the preferred additives at progressively higher manganese contents ranging from 0.01 to 0.04 mole Mui'2 per mole magnesium aluminate-gallate even at 50% substitution of Al for Ga (y=0.05). The relative performance for SrHPO4 addition is also shown.

Table 6 shows that even with a substitution of Al for Ga of y=0.7, and very high Mnt2 content, that stabilizers containing both calcium and phosphate ions are effective to increase brightness and oxidation resistance.

Table 7 shows the beneficial effects of calcium addi- 1 1 tion over a wide range of magnesium variation. I have found that the alkaline earth addition is useful over a range of magnesium extending from about 0.1 to about 1.2 mole Mg per mole aluminate gallate.

The date in Table 8 shows that of the various additives therein listed at 0.18 mole concentration only those containing the phosphate ion as the only stabilizer additive or in conjunction with an alkaline earth ion exhibited higher brightness as compared with the same basic phosphor containing no additive at firing temperature of 1250 C. and 1400 C. At the 0.18 mole concentration and 1250 C. firing temperature, the CaCO3 and CaSO4 additives exhibited lower powder brightness but reference to Table 3 indicates that lower concentrations of CaCO3 additive and a l400 C. firing temperature provides effective Ca+2 ion stabilization.

In Table 9 are reported the results obtained with (NH4)2HPO4 doping which are also plotted graphically in FIG. 1 to establish the concentration limits for the phosphate additives. It will be evident from these results that improved brightness phosphors can be prepared at a 1250 C. firing temperature if the phosphate ion concentration lies between 7.5 102-2.1 101 mole phosphate ion per mole magnesium aluminate-gallate.

In Table 10 there are reported the results obtained with PO.,n3 ion doping; obtained by adding MgNH4PO4 at the indicated proportions to the same basic phosphor composition prior to firing. The x value in said table represents the total Mg obtained from the MgCO3 and MgNHlPO.,l constituents used in the phosphor preparation. Table II reports the comparable results obtained with variation of the Mg+2 ion concentration ranging from .4Z-1.4 moles Mg per mole magnesium aluminate-gallate when .02 moles Cai2 ion per mole magnesium aluminate-gallate is added as a cool white halophosphor. The brightness measurements reported in both tables are plotted in FIG. 3 to establish that useful magnesium aluminate-gallate phosphors of the present invention are obtained between the limits of 1X l01-1.3 mole Mg+2 ion per mole magnesium aluminate-gallate with the present additives.

Table 12 provides additional preparations of phosphor wherein x varies between .18 and .85 and further containing various minor amounts of the CaHPO4 additive. It can be seen from this table that a shift in the emission peak response of the phosphor from 512 nanometers to 506 nanometers takes place with increasing additive concentration within the limits hereinbefore set forth. A reference to the emission peak response results in Table l which indicate the extent of color shift attributable to increasing A1 substitution in the phosphor serves to illustrate the manner in which an increase of the additive concentration can offset the emission peak shift otherwise obtained.

In accordance with my invention, I add a minor proportion of the stabilizer additive to magnesium aluminategallate phosphor activated by manganese sufficient to maintain brightness at least equal to that occurring with lower substitution of Al for Ga. In general, the useful range of a stabilizer additive M extends from a small but efective amount, that is 1 l0-5 mole per mole of magnesium aluminate-gallate to about 3 101 mole per mole magnesium aluminate-gallate. The upper concentration limit of additive can surprisingly exceed that amount forming a solid solution in the host phosphor matrix at the indicated ring temperatures. The useful additive range is further illustrated in the accompanying FIGS. 1-3 which plot the effect upon brightness for phosphate ion as the only stabilizer ion and combinations of phosphate ion with either Ca't2 ion or Mgt2 ion. More particularly, the range of phosphate ion is plotted in FIG. 1 for various additions of (NH4)2 HPO4 in a phosphor prepared by air ring at 1250 C. In FIG. 2 there is plotted the brightness results for various ranges of CW calcium halophosphate phosphor additive to the same phosphor composition employed in FIG. l. In FIG. 3 there is shown the effect upon brightness of the Mgt2 ion concentration with the dashed line plot representing an addition of .02 mole CW halophosphate phosphor to various basic phosphor compositions represented by The solid line plot in FIG. 3 represents .18 mole concentration of MgNH4PO4 in the same basic phosphor cornposition. From a consideration of all these results taken together, it can be seen that a combination of the phosphate ion with Ca+2 ion is the most preferred additive to stabilize a magnesium aluminate-gallate phosphor from brightness loss when the phosphor is heated in the air after preparation. It can also be noted from these results that high brightness phosphors are obtained if the MgJf2 ion concentration of the phosphor lies between the rather wide limits of 1 lO-1l.2 mole Mg per mole magnesium aluminate-gallate when the phosphate ion or a combined CM2-P053 ion additive is used. With reference to the following general phosphor formula:

The invention is useful at least within the limits of x between about 0.1 to 1.2, y between about 0.1 and 0.7, z between about .01 and 0.1, and w between about 1 105 and 3 X 10*1.

METHOD OF PREPARATION By way of example, a phosphor according to the invention wherein y=0.3 may be prepared using the following phosphor ingredients:

Molar formula of ingredients before tiring:

Mgo.a5A1o.6Ga1.40s.s5Mn.oaCa.oo5Pa43x10'3 After thorough mixing, the ingredients are rst fired 4 hours at 1250 C. in air to carry out most of the inherently sluggish reaction of the oxides which forms the magnesium aluminum-gallate. The diffusion of the cations is rather slow despite the high firing temperature, and I have found it desirable to remix or regrind the first fired product in a mortar or ball mill and then to re again. The second ring is also done at 1250 C. in the air for a more extended period, suitably 16 to 18 hours. Surprisiigly, even this rather extreme heat treatment does not cause the phosphor to sinter excessively, and the cooled powder can be ground and screened quite readily. A third and nal firing is done at 1200 C. for 2 hours in a reducing atmosphere, suitably nitrogen containing about 0.5% hydrogen. It is during this last step that some of the gallium is lost.

In my experience, this method has consistently produced powders which are whiter when viewed in daylight and brighter' when viewed under exciting ultraviolet radiation than are powders produced by the procedures described in the references mentioned earlier. On the other hand, my experience with preparations of a .03Mn+2 activated Mg,85Ga1 4,Al0 6O3,85 phosphor containing .067 molar concentration CaJf2-PO4-3 ion obtained from CaHPO4 addition indicates that powder brightness varies with the air ring temperature. More particularly, a firing temperature of 1250 C. produces as good `a phosphor as can be produced with a considerably higher 1400 C. firing temperature if no additive is used. In fact,'the

l13 oxidation resistance for the 1250 C. air red product was found to be significantly better than test results upon a phosphor fired at 1400 C., but containing no additive as was earlier shown.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An improved magnesium aluminate gallate phosphor activated with manganese which further contains a minor proportion of stabilizer additive MW as a solid solution in the phosphor matrix to avoid brightness loss when the phosphor is heated in air, said stabilizer additive consisting essentially of an alkaline earth metal ion selected from the group of calcium, strontium and barium with a phosphate ion, wherein the mole ratio of alkaline earth metal ion to phosphate ion is between approximately 1-1.6, said phosphor having the formulationz't wherein x is between about 0.1 to 1.2 wherein y is between about 0.1 and 0.7 wherein z is between about .01 and 0.1 and w is between about 1 105 and 3X101.

2. A phosphor as in claim 1 wherein the phosphate ion is present at a mole fraction between 7.5 X10"2 and References Cited UNITED STATES PATENTS 3,499,843 3/ 1970 Brown et al. 252--30L4 R 3,632,522 1/1972 McAllister 252-301.4 R

3,635,833 1/1972 Datta 252-301.4 R

3,723,339 3/ 1973 Wamnaker et al. 252-301.4 R

FOREIGN PATENTS 465,210 5/1950 Canada 252-3014 R JACK COOPER, Primary Examiner U.S. Cl. X.R. 252-3014 R 

